Summary

Is there any equipment that I can rent 'inexpensively' (less than $400) that would allow 1-2 people to accurately (+/- 6") capture the topography of hilly terrain of perhaps 250' on a side in an afternoon?

Details

My wife and I are about to embark upon a redesign of the landscape around our home in the mountains. Our lot started out on what's generally a 1:3 slope, and this has (of course) been changed in many interesting ways during building. There are small hills, patios, semi-flattened areas followed by large falloffs.

As part of our designing, we want to capture exactly what the landscape looks like now, digitally. (Then we'll sculpt in the computer what we want, taking into account existing boundaries and surrounding contours, and see roughly how much dirt we need or will need to remove.)

We performed a "ghetto" survey this weekend with strings and poles, roughly sampling a grid of elevations every 10'. The results we got produced a reasonable-looking representation of the terrain. However, the 10' sampling was a bit too coarse for my tastes and—more importantly—we were only able to sample about 1/4 of the area we need before our measuring poles weren't tall enough or we ran out of reference objects.

So... What hardware exists that I can rent to make this task easier? Ideally, I'd like to take a pole, walk all over the property, and every few feet stick it on the ground, press a button, hear it go "beep!" and have it record an XYZ sample that is accurate within +/- 6". After doing this for a couple hours I'd plug it into the computer and download some DEM, CSV, or other accessible data of all the points in a non-proprietary format.

It looks like Trimble offers some neat gadgets in this arena, and I see that some companies rent this sort of gear out, but as I'm not a landscape survey engineer professional, I cannot figure out exactly which, if any, products meet my needs.

Can someone who knows this product space please help suggest what I should be looking for?

  • 2
    You might look at gis.stackexchange.com. – Jay Bazuzi Mar 8 '11 at 2:47
  • One way to compare the height of two objects you can't get line of sight between is the GPS on your phone. We used this to compare the elevation of our house and a neighbour's house as part of considering a point-to-point wireless solution. – Kate Gregory Sep 18 '12 at 12:48
up vote 8 down vote accepted

Option #1:

  1. Find a few objects (house, trees, etc.) that, together, allow at least one of them to be level line-of sight from anywhere in the yard.

  2. Tape a laser pointer on the end of a level (taped so you can use the level as a sort of monopod resting on the ground).

  3. Move around the yard, hold the level level, and point the laser at one of the objects. Have someone at the object use a measuring tape to record the measurement. Subtract the length of your level.

  4. Once you have all of your measurements, figure out the elevation offsets of the objects in relation to one another and offset measurements against them accordingly.

Option #2: Use a photogrammetry program like PhotoModeler (http://www.photomodeler.com/) to combine photographs taken using a tripod and a digital camera from different vantage points. Of course, these apps are incredibly expensive, probably cost more than the gadgets you mentioned. Unless you happen to already own a license to one of the AutoCAD products that gives you access to AutoDesk's photogrammetry app, ImageModeler 2009 (http://usa.autodesk.com/adsk/servlet/pc/index?id=11390028&siteID=123112).

Buy or rent a laser level, one that sends out a disc of light all in a level plane. Set it up a foot off the ground at the high point.

Walk around with a yardstick (or two yardsticks taped together, depending on how much slope there is). At each point on your grid, record where on the yardstick the laser hits. You may need to do this at night to see the laser line.

Enter your data into one of the programs mentioned in the other answers.

With the self-leveling laser lines, you can eliminate some of the annoying steps from other solutions. Measuring out your grid is still annoying, however.

Edit: Reading the question again I see I haven't actually addressed your major pain, namely, having a huge slope. You'll need a tape measure with good standoff, or a much longer pole (roof rake with tape markings on it?) to get the depths at these points, and measuring the grid is even more annoying. You'll probably need to survey these areas in chunks, staking the laser into a new place in the ground at the start of each area, and stitch them together.

  • If you have two laser levels, one for height, and the other to give you a straight line, then you'd only need something for distance (ie, a long tape measure, although droop might throw off your measurements at longer distances). If you got all of your lines parallel, and used two people (one to re-position the second laser and record the values while the other person moved from point to point and measured), you might be able to get it done fairly quickly. – Joe Mar 15 '11 at 14:04
  • 1
    If you're willing to buy a second laser, get one that measures distance and use it... – Alex Feinman Mar 15 '11 at 14:22
  • you don't have to buy (although, they are rather useful), as you can rent them from most tool supply places. (at least, the places near me have 'em). – Joe Mar 15 '11 at 15:10

I'm wondering if a good DSLR camera on a solid tripod might make a Quick and Dirty leveling transit.

The basic technique using a leveling transit and Rod is:

  1. Pick a zero location.
  2. Set up transit away from that location, where the head is higher than your zero.
  3. Put graduated rod (usually red and white 1 cm marks) on the zero.
  4. Sight the rod, and record the measurement. This give Height of Instrument (Hi).
  5. Repeat the sighting and recording at every point you want to measure.
  6. Once you've done everything you can from one location, move the instrument to new territory, sighting back to a known station to get the new Hi.

The math:

  • Assume an elevation of Zero for your first benchmark.
  • Hi = reading on rod.
  • All other stations from that setup point are Elev = Reading - Hi (relative to benchmark)
  • To determine Hi2 from a known station, Hi2 = Elev(station) + Reading.
  • 5
    When I worked as a summer as a survey tech, we always rocked the level rods (graduated rod) forward and backward a few degrees and took the max reading. Much quicker than making sure it's completely level before sighting. – Doresoom Mar 10 '11 at 15:49

I was faced with the same problem - wanting to terrace my sloping back yard to make it more usable. I needed to know where to make the terrace divisions to avoid having to remove or add soil from the site, and to know how many blocks to buy. Here's what I did:

Method Summary:

  1. Collect topography in spherical coordinates relative to compass readings and gravitational level using as many origins as needed to survey the area of interest.
  2. In excel, convert to Cartesian coordinates
  3. Translate multiple data sets to a common reference frame
  4. Sort the data from lowest to highest Z
  5. Plot the data in multiple series according to desired contour line resolution
  6. Use trend lines to fill in the contour lines, or draw by hand.

Results:

Cost was zero as I already had the laser tape, phone and tripod. A laser tape costs between $50 and $150 depending on distance and fancy features. Mine was $100.

Accuracy: Looks like about 6" based on data noise. But I honestly didn't work very hard at being careful since I didn't want to take a lot of time if the process had some unforeseen hang up looming. I didn't even cinch down the laser and phone tight to the Masonite. They were pretty loose. The laser origin was not centered at the center of rotation of the tripod which contributes to error. Didn't always hit the ground with the laser due to long grass, and leaves and some bushes. As far as the Android accuracy, not sure, but it would be easy to do some tests to find out as all we care about really is local relative accuracy. That is, if my phone is off by 10 degrees, I don't care as long as one degree difference in orientation reads as one degree reading difference.

Time: About 2 hours to collect 200 data points from three locations.

Area covered was about 60 feet wide by 20 feet deep with a z variation of about 8 feet.

Details:

  1. Collect the data. I used a cheap camera tripod that had tilt and pan, a Bosch laser tape, and my Android smart phone with a compass level app installed. I used a piece of Masonite to make a platform to attach to the tripod, and secured the phone and laser tape to the Masonite with zip ties. Pan and tilt away, recording compass heading and tilt from the phone and distance from the laser tape in an excel spread sheet. I included a fairly small (aka unambiguous) reference point in the data set that I could see from the next location I was moving my tripod to. Repeat several times to go around the yard. (You don't need to use the same original reference point, just need a reference point between adjacent data collection positions.)

  2. In excel, convert the data from spherical coordinates, which is what you have when you collect pan or compass angle, pitch angle, and distance from the collection point, to Cartesian coordinates or (x,y,z). (Simple formulas available on line for the conversion.)

  3. Translate to a common reference frame. Each time I moved my tripod, I would collect a new data set that had its own origin and of course I only want one. Conveniently compass headings and tilt are absolute, that is, they don't change when I move the tripod. That means all my data sets share common pan and tilt reference frames, so my data only has to be translated, no matrix multiplication required! All I had to do take the difference in x,y, and z between data sets, for my unambiguous reference point, and add that difference to all coordinates in the secondary set to translate it to the primary data set. Do this translation as many times as needed to move the last data set to the next to the last, then to the next, etc. and finally to the primary set. Now all the data is in one common reference frame. (This can be done in one step that is the sum of all the translations.)

  4. Use the Sort function to rearrange the data by z values, smallest to largest.

  5. Use the scatter plot chart to plot the x,y data in a series of plots based on z ranges. For example group all data with z between 0 and 1 foot, 1 to 2, etc and plot them all on the same graph. Each plot represents an isocontour (there's a better word for that, right?).

  6. Use the trend line function to draw contour lines through the data sets. I used the 6th degree polygon function to draw the line which might not be agile enough for a lot of data sets.

New information##

I did a little research into other methods for creating topographical maps of my yard. The classic method is to use a theodolite, poles, a tape and plumb bobs. The theodolite is just a telescope that registers tilt and pan (pitch and yaw if you like) very accurately. Now days, people use totaling stations which measure pitch and yaw, and distance all at once, which are spherical coordinates, from which you get 3D coordinates after a little arithmetic. That’s exactly what I’m doing with my laser tape and phone. I’ve added a photo of the set up.

I think the best accuracy you can expect with this flimsy setup in on the order of a few inches. The problems are mainly two.

  1. Compass errors.
  2. Alignments and rigidity.

The laser tape is pretty good, fractions of an inch, and the pitch measurement is pretty good, .1 deg or so. The compass is pretty bad. The sensor in the phone drifts pretty fast and is easily perturbed by any ferrous metal or electronics, thus the roughly 12” separation between the phone and the laser tape. Unfortunately, the separation made my setup pretty flimsy.

But, it does give me a usable picture of my back yard.

This data was collected in the dark, raining, and the phone was right next to the laser tape. It could be greatly improved by using the phone only for pitch, and adding a better compass, and a more ridged platform and by doing some cursory alignments between the laser and pitch axis of the tripod.

I ran several more accuracy tests by picking some points around my yard and inside my house where I could calculate point positions and separation distances with my set up, then compare with direct laser tape measurements.

With phone, laser tape and camera tripod, with a stiffer mount for the laser and phone, and with the laser aligned with the pitch axis on the tripod, it looks like you could get about +/-8” in the horizontal plane, and +/-1” vertically at 20’.

Swap out the phone compass for a protractor and the errors reduced to +/-1” in 3D. I used a carpenter’s sight level as my protractor that reads in degrees.

Broke down and bought a used theodolite ($260) and the errors reduced to about +/-3/8” in 3D. And this I would attribute to the fact I was holding the laser tape by hand over the theodolite, trying to position the back of the tape at the center of rotation of the viewer, and point at the spot I was looking at through the viewer.

If you were to ask me how to create a topo map of your yard, I’d suggest the laser tape, smart phone, and carpenter’s level, one that allows you to pitch and yaw and read angles. Transit levels are giving way to the laser levels so you can get them on ebay for under $100.

  • Great answer and write-up! I think it would be great if you could include some pictures or diagrams, both of your setup and results. – Phrogz Nov 16 '17 at 13:20
  • Thanks Phrogz. Sure. I'll put together some pics and thoughts. – Bob T. Nov 18 '17 at 18:38

I'd say don't use laser levels, just go old school style, rent a rod and level (I don't know how much they are because I work for an engineering company so I just borrow them for a weekend). Rods come in quite large sizes (I usually borrow our 25ft ones) so you wouldn't have to set up the level too much, follow the advice of the dslr idea but using a regular level instead, much easier. You can spray paint the ground at predetermined marks you want to get the elevations of or you could also pound stakes (small wood pieces or anything easily distinguishable and be able to number them) into the ground so that they are always easy to remember exactly where which elevations are.

And just to explain more indepth of what he was talking about if it didn't make sense. First elevation you shoot (where the rod is) call the elevation 100ft (easier to start with so you don't go into the negatives if you start with 0) if you shoot 5ft on the rod, your height of instrument is 105ft. If the next shot you take says 20 ft on the rod that means that the elevation at the rod would be 85ft. You keep the rod on that spot and set up the level again at a lower part of the yard, so you can read only a bit on the rod, so with the rod still in the same place you read 2ft on the rod at the new location for the level. The height of instrument is now 87ft, and you can continue on using that. You just need to set up the level again every time that you are close to the end of the rod.. Good luck

It sounds like you are willing to invest some real time in this, the pole and string method is a good start, to take this to a very detailed scale you almost need to survey they grounds from a fixed point (like close to your house) with someone else holding a maker pole in a lot of different places in the yard.

You see government workers doing this all the time when they are surveying roads and highways. With good measurments of distance and percice angle measurments and quite a bit of math (a good excel sheet should help here) this can be done. they do sell survey equpment on amazon, but you can probably rent it more cheaply localy.

http://www.amazon.com/CST-berger-55-SAL20ND-Automatic-Level/dp/B000YBJ8VW/ref=sr_1_2?ie=UTF8&qid=1299764646&sr=8-2

Your Answer

 
discard

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.